1. Field of the Invention
The present invention relates to a paper container and method of manufacturing it that is used as a container for food products or plant pot etc. In more detail, it relates to a paper container and method of manufacturing it having a deep bottom and formed by folding a single-sheet blank.
2. Description of the Related Art
Conventionally, for the distribution of food products etc., plastic containers, which are easily molded, are frequently used. However, recently, on account of problems concerning elution of environmental hormones or disposal processing after use, the use of paper containers is being re-evaluated. As methods of manufacturing paper containers, the method of sticking together and the papermaking method etc. are well known. In the former i.e. the sticking-together method, for example raw-material paper sheets that have been subjected to laminating processing are employed to separately mould blanks which are used for forming the trunk and the bottom of the container; these two are then united by hot pressure fixing in a metal mold.
In the latter i.e. the paper-making method, the paper fibers are dispersed in water and the basic shape of the container is produced by filtering this colloidal solution using a paper-making mesh of prescribed shape and dewatering; the paper container is then manufactured by hot pressing or by drying this using a current of hot air. These methods had the drawbacks that the number of steps necessary was large, making them costly, and that the containers obtained had little resistance to water and so could not be employed for containers that need to be waterproof, such as containers for drinks or plant pots.
Also, the drawing method of integrally forming a paper container from a single-sheet blank is conventionally known and is commonly employed. With this drawing method, waterproof containers can be manufactured efficiently and at low cost by for example using blanks that have been subjected to laminating processing.
This drawing method has the advantage that a waterproof product can be produced comparatively easily with a small number of steps, since it is integrally formed from a single-sheet blank. However, setting the conditions for the processing is extraordinarily difficult and in particular there was the difficulty that the blank tended to tear in the case of deep drawing. Consequently, conventional paper containers obtained by drawing were of shallow bottom, which restricted their application.
The present invention was made in view of the technical background described above and achieves the following object.
An object of the present invention is to provide a paper container of deep bottom integrally formed from a single-sheet blank, and a method of manufacturing it.
In a method of manufacturing a paper container of deep bottom integrally formed from a single-sheet blank, a further object of the present invention is to provide a method of calculating the development plan of the paper container.
In order to achieve the above object of the present invention, a method of manufacturing a paper container is provided wherein a blank is obtained by cutting a single-sheet of raw-material paper to a prescribed shape and an annular rule line constituting a regular polygonal shape is formed in the middle of this blank and designated as the bottom face of the paper container. After this, divided faces on the outside of the peripheral wall face constituting the peripheral wall face of the paper container and inner pleated faces on the inside are formed on the outside of the annular rule line. The divided faces are of the same number as the number of corners of the bottom face, and are arranged to extend from each side of the annular rule line to the outside. The blank regions between the divided faces constitute the inner pleated faces, the inner wall faces being bisected by axes of symmetry extending dividing the inner pleated faces into two symmetrical portions from the corners of the annular rule line. After this, the inside edges of each divided face are brought together by folding the annular rule line while folding each inner pleated face in two along the axis of symmetry, and the region inside the annular rule line is made to constitute the bottom face by folding over the inner pleated faces on each divided face.
If the height of the paper container, the radius of the uppermost face of the paper container, the radius of the lowermost face of the paper container, and the number of corners of the bottom face of the paper container are determined, a paper container of any desired shape with an open upper surface can be produced. The condition of the paper at the rim of the uppermost face of the paper container can be made to be a single sheet, or three sheets, or, if appropriate, five sheets, at particular locations.
Next, embodiments of the present invention will be described.